1. Field of the Disclosure
The present disclosure relates to a light amplifier and a laser processing device, and particularly to a technique of stably generating a light pulse from a fiber amplifier in an MOPA (Master Oscillator and Power Amplifier) system.
2. Background Information
In laser processing devices, the laser beam power influences the processing quality. To address the problem, techniques of controlling the power of laser beam emitted from the laser processing device have been proposed.
For example, Japanese Patent Laid-Open No. 2000-340872 discloses a laser processing device including a fiber containing a rare-earth element and a laser light source for exciting the rare-earth element. The laser light source includes a first semiconductor laser which is sequentially driven to emit low powered light and a second semiconductor laser which is pulse-driven to emit high powered light. During a non-emission period, the rare-element doped fiber is made transition to a preliminary excited state by the exciting light emitted from the first semiconductor laser. During a processing period, the rare-element doped fiber is made transition to a highly excited state by the exciting light emitted from the second semiconductor laser. Since signal light is incident on the highly excited rare-element doped fiber, the high powered laser beam is emitted from the rare-earth doped fiber. The low powered laser beam preliminary excites the rare-earth doped fiber, and therefore, the pulse output during the processing period is stabilized.
On the other hand, Japanese Patent Laid-Open No. 2010-10274 discloses configuration for measuring the average power and the peak power of a laser pulse which is output from a fiber laser oscillator and feeding back the measurements to an LD (laser diode) drive circuit.
Further, Japanese-Patent Laid-Open No. 2010-171131, for example, discloses that the laser light source for emitting seed light to be incident on the fiber laser emits pulsed light during the main radiation period and emits substantially continuous light during the preliminary radiation period. The power of the continuous light is weaker than the peak power of the pulsed light. Japanese-Patent Laid-Open No. 2010-171131 also discloses that the power of the exciting light in the preliminary radiation period is lowered below the power of the exciting light in the main radiation period.
The laser processing device disclosed in Japanese Patent Laid-Open No. 2000-340872 uses a fiber laser. The fiber laser is capable of setting respective conditions for the laser beam such as (1) the pulse repetition frequency, (2) the pulse width, and (3) the pulse power independent from each other. On the other hand, the optimal output value of the low powered laser beam may depend on these conditions. When the output value of the low powered laser beam is not optimal, the strength of the first pulses is different from the strength of the stabilized pulses. That might degrade the processing quality.
The method disclosed in Japanese Patent Laid-Open No. 2010-10274 uses the average power of the laser pulse for a feedback control. Therefore, it is difficult to perform the control for each pulse.
In the configuration disclosed in Japanese Patent Laid-Open No. 2010-171131, the amplified light is emitted from the light amplifying fiber not only during the main radiation period but also during the preliminary radiation period.
With the configuration, the amplified light is emitted from the light amplifying fiber during the preliminary radiation period, which can prevent the optical fiber from accumulating too much energy during the preliminary radiation period. Accordingly, the power of the first pulses can be controlled below the excessive level during the main radiation period. However, Japanese Patent Laid-Open No. 2010-171131 does not specifically disclose the configuration for ensuring the above described control on the power of the pulse.
An object of the present disclosure is to provide a light amplifier which is capable of stably outputting a laser pulse from the first time and a laser processing device.